Improved Direct Torque Control of Induction Motor

ABSTRACT:

Control of induction motor is most precisely required in many high performance applications. With the development in power electronic field various control methods for control of induction motor have been developed. Among these Direct torque control (DTC) seems to be particularly interesting, being independent of machine rotor parameters and requiring no speed or position sensors. In addition to the simple structure it also allows a good torque control in transient and steady state conditions. The disadvantage of using DTC is that it results in high torque and flux ripple and variable switching frequency of voltage source inverter, owing to the use of hysteresis controllers for torque and flux loop. In order to overcome these problems, various methods have been proposed by several researchers like variable hysteresis band comparators, space vector modulation, predictive control schemes and intelligent control techniques. However these methods have diminished the main feature of DTC that is simple control structure. This report presents constant switching frequency based torque and flux controllers to replace conventional hysteresis based controllers where almost fixed switching frequency with reduced torque and flux ripple is obtained by comparing the triangular waveforms with the compensated error signals

KEYWORDS:

                                 1.3-phase VSI

                                 2. torque controller

                                 3. flux controller

SOFTWARE:  MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig.1. Block diagram of conventional DTC method

Fig.2. MATLAB/SIMULINK Model of the DTC Drive

EXPECTED SIMULATION RESULTS:

            

Fig.3. Torque response (a) Conventional DTC scheme (b) Improved DTC Scheme

 Fig.4. Speed and Torque response for (a) Conventional DTC scheme (b) Improved DTC scheme

Fig.5. Circular flux locus (a) conventional DTC scheme (b) Improved DTC scheme

Fig.6. 3-phase line-line voltages and currents (a) Conventional DTC scheme (b) Improved DTC scheme

CONCLUSION:

In this paper a detailed comparison between the conventional DTC and improved DTC scheme is made with help of some Matlab simulation results and hence it is shown that a significant reduction in torque and flux ripple can be achieved with the improved DTC scheme also with improved controllers the switching frequency which is constant can be varied by varying the frequency of the triangular carrier waveforms of the torque controllers

REFERENCES:

[1] I. Takahashi and T. Noguchi, “A new quick-response and high efficiency control strategy of an induction motor,” IEEE Trans. Ind. Appl., vol. IA-22,no. 5, pp. 820–827, Sep.–Oct. 1986.

[2] J-K. Kang, D-W Chung, S. K. Sul, (2001) “Analysis and prediction of inverter switching frequency in direct torque control of induction machine based on hysteresis bands and machine parameters”, IEEE Transactions on Industrial Electronics, Vol. 48, No. 3, pp. 545-553.

[3] D.Casadei, G.Gandi,G.Serra,A.Tani,(1994)“Switching strategies in direct torque control of induction machines,” in Proc. of ICEM’94, Paris (F), pp. 204-209.

[4] J-K. Kang, D-W Chung and S.K. Sul, (1999) “Direct torque control of induction machine with variable amplitude control of flux and torque hysteresis bands”, International Conference on Electric Machines and Drives IEMD’99,pp.640-642.

[5] Vanja Ambrozic, Giuseppe S. Buja, and Roberto Menis, ”Band- Constrained Technique for Direct Torque Control of Induction Motor”, IEEE Trans. On industrial electronics , vol. 51, no. 4, august 2004, pp.776-784

A New Hybrid Active Neutral Point Clamped Flying Capacitor Multilevel Inverter

 ABSTRACT:

This paper proposes a new five-level hybrid topology combining features of neutral point clamped and flying capacitor inverters. The proposed topology provides a tradeoff between different component counts to achieve a good loss distribution, avoid direct series connection of semiconductor devices, keep the balanced operation of dc-link capacitors while keeping the number of costly components such as capacitors and switches low. The required modulation strategy is developed and the operation of the proposed topology is studied. The features of the proposed topology are investigated and compared to other available topologies. Simulation results are provided to verify the performance of the converter for medium voltage applications

KEYWORDS:

              1 .Multilevel Inverter,

              2. Flying Capacitor,

              3. Active Neutral Point Clamped,

              4. Diode Clamped.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. A phase leg of the proposed 5-level hybrid topology.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results. (a) Phase voltage (b) Line voltage (c) Flying capacitor voltages (d) Load current

frequency 5kHz. The dc-link voltage is set at 18kV and flying capacitors are 330μF. It can be seen that even without an RLC balance booster, the capacitor voltage errors are limited to less than 4%.

CONCLUSION:

A new hybrid 5-level inverter topology and modulation technique is proposed. Compared to 5-level ANPC as the most similar topology, this new topology requires two less switches at the cost of an additional capacitor and six diodes. However, since the capacitors still see the switching frequency and their size remain the same, it is expected to reduce the inverter’s

total cost. Also, unlike 5-level ANPC, all switches must withstand the same voltage which eliminates the need for series connection of switches and associated simultaneous turn on

and off problem. Good loss distribution among switches can increase the inverters rated power    or provide higher switching frequency and smaller capacitor size.

REFERENCES:

[1] H. Abu-Rub, J. Holtz, and J. Rodriguez, “Medium-Voltage Multilevel Converters—State of the Art, Challenges, and Requirements in Industrial Applications,” IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 2581–2596, Aug. 2010.

[2] S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, J. Rodriguez, M. A. Pérez, and J. I. Leon, “Recent Advances and Industrial Applications of Multilevel Converters,” IEEE Trans. Ind. Electron., vol. 57, no. 8, pp. 2553–2580, Aug. 2010.

[3] M. Malinowski, K. Gopakumar, J. Rodriguez, and M. A. Pérez, “A Survey on Cascaded Multilevel Inverters,” IEEE Trans. Ind. Electron., vol. 57, no. 7, pp. 2197–2206, Jul. 2010.

[4] J. Rodriguez, “Multilevel inverters: a survey of topologies, controls, and applications,” IEEE Trans. Ind. Electron., vol. 49, no. 4, pp. 724–738, Aug. 2002.

[5] J. Rodriguez, S. Bernet, P. K. Steimer, and I. E. Lizama, “A Survey on Neutral-Point-Clamped Inverters,” IEEE Trans. Ind. Electron., vol. 57, no. 7, pp. 2219–2230, Jul. 2010.

Direct Torque Control of Induction Motor Drive With Flux Optimization

ABSTRACT:

MATLAB / SIMULINK implementation of the Direct Torque Control Scheme for induction motors is presented in this paper. Direct Torque Control (DTC) is an advanced control technique with fast and dynamic torque response. The scheme is intuitive and easy to understand as a modular approach is followed. A comparison between the computed and the reference values of the stator flux and electromagnetic torque is performed. The digital outputs of the comparators are fed to hysteresis type controllers. To limit the flux and torque within a predefined band, the hysteresis controllers generate the necessary control signals. The knowledge about the two hysteresis controller outputs along with the location of the stator flux space vector in a two dimensional complex plane determines the state of the Voltage Source Inverter (VSI). The output of the VSI is fed to the induction motor model. A flux optimization algorithm is added to the scheme to achieve maximum efficiency. The output torque and flux of the machine in the two schemes are presented and compared

KEYWORDS:

                          1.Direct Torque Control,

                          2. Induction Motor,

                          3. Flux Optimization

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Figure 1: Block Diagram of Conventional DTC Scheme

 

Figure 2: Block Diagram of the Flux Optimized DTC Scheme

EXPECTED SIMULATION RESULTS:

                              

Figure 3: Stator d-q flux space vector without flux optimization                     

                                   

 Figure 4: Stator d-q flux space vector with flux  optimization

                                  

Figure 5: Variation of Stator Flux – Conventional  DTC Scheme                                                                   

                                    

  Fig 6: Variation of Stator Flux - Optimized DTC scheme

                                                   

                                                            

      

Figure 7: Variation of Mechanical Speed – Conventional  optimized DTC scheme    

   

                                     

 Figure 8: Variation of Mechanical Speed - Optimized DTC scheme

                                         

Figure 9: Electromagnetic Torque - Conventional DTC

             

                                            

Figure 10: Electromagnetic Torque - Optimized  DTC

                                   

Figure 11: Percentage Efficiency of Flux Optimized DTC

CONCLUSION:

In this paper, DTC for an induction motor drive has been shown along with flux optimization algorithm. DTC is a high performance, robust control structure. A comparative analysis of the two DTC schemes, with and without flux optimization algorithm has been presented. With flux optimization implementation, it is observed that the efficiency of the about 87 % has been obtained. MATLAB simulation of a 15 Hp IM drive has been presented to confirm the results.

REFERENCES:

[1] Werner Leonhard. Control of Electric Drives. Springer-Verlag Berlin Heidelberg, 1996.

[2] F. Blaschke. “The Principle of Field Orientation as Applied to The New Transvector Closed Loop Control System for Rotating Field Machines”. Siemens Review, pages 217–220, 1972.

[3] K. Hasse. “On The Dynamic Behavior of Induction Machines Driven by Variable Frequency and Voltage Sources”. ETZ Archive, pages 77–81., 1968.

[4] I. Takahashi and T Nogushi. “A New Quick Reponse and High Efficiency Control Strategy of an Induction Motor”. IEEE Trans. Industry Applications, IA -22:820–827, 1986.

[5] M. Depenbrock. “Direct Self Control (DSC) of inverter-fed induction machines”. IEEE Trans. Power Electronics, 3(4):420–429, 1988

Control Strategies for Wind-Farm-Based Smart Grid System

ABSTRACT:

To incorporate the abundance of renewable energy into the power system, it is required to reconfigure the energy system. An intelligent power grid such as the smart grid is the solution for future energy demand. Among several renewable sources, the wind energy conversion system (WECS) is the rapidly growing source of energy, which is considered as the backbone of renewable energy and the smart grid. This paper deals with control strategies of distributed wind farms that are connected to smart houses for a smart grid application. A grid-side energy storage system is considered to deliver smooth power to the system. Stable control strategies under the line fault condition are also discussed in this paper. The surplus power of the smart houses is sent back to the power grid, and a house owner can benefit by selling the extra power to the power company. The detailed modeling and control strategies of an intelligent power system are demonstrated in this paper. The effectiveness of the proposedsystem is verified by the extensive numerical simulation results.

KEYWORDS:

1. Doubly fed induction generator

          2. Electric double layer capacitor (EDL)

                                                       3. Fault condition

                                                       4.Power smoothing smart grid

                                                       5.Smart house

                                                       6. Wind farm.

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

      

Fig. 1. Proposed system configuration

EXPECTED SIMULATION RESULTS:

                                 

                                         

Fig. 2. Simulation results under the normal condition. (a) Wind speed. (b) Rotational speed of the wind turbine. (c) Wind farm output powers. (d) Different powers of the system. (e) Output power of the EDLC. (f) DC-link voltage of the EDLC. (g) Power of house group-1. (h) Power of house group-2. (i) Power of transformer-1. (j) Power of transformer-2.

 

Fig. 3. Simulation results under the fault condition. (a) Wind speed. (b) Rotor speed. (c) Output power of the wind farm. (d) DC-link voltage of the wind turbine. (e) DC-link voltage of the EDLC. (f) Terminal voltage of the EDLC. (g) Line power of the system.

CONCLUSION:

A wind-farm-based smart grid system coordinated with smart houses has been proposed. Wind velocity is a fluctuating resource, and the generated power of the wind turbine is cubic proportional to the wind speed. Therefore, the output power of the wind turbine is fluctuated. In this paper, an EDLC energy storage is applied to generate a smooth line power for the smart grid system. The line power can be smoothed by the EDLC system extensively. In addition, a stable operation can be performed at the fault condition through the chopper circuit approaches. From the simulation results, the effectiveness of the proposed method is verified.

REFERENCES:

[1] P. Yi, A. Iwayemi, and C. Zhou, “Developing ZigBee deployment guideline under WiFi interference for smart grid applications,” IEEE Trans. Smart Grid, vol. 2, no. 1, pp. 110–120, Mar. 2011.

[2] A. Ipakchi and F. Albuyeh, “Grid of the future,” IEEE Power Energy Mag., vol. 7, no. 2, pp. 52–62, Mar./Apr. 2009.

[3] G. Mandic, A. Nasiri, E. Muljadi, and F. Oyague, “Active torque control for gearbox load reduction in a variable-speed wind turbine,” IEEE Trans. Ind. Appl., vol. 48, no. 6, pp. 2424–2432, Nov./Dec. 2012.

[4] H. Jagau, M. A. Khan, and P. S. Barendse, “Design of a sustainable wind generator system using redundant materials,” IEEE Trans. Ind. Appl., vol. 48, no. 6, pp. 1827–1837, Nov./Dec. 2012.

[5] A.M. Howlader et al., “A minimal order observer based frequency control strategy for an integrated wind–battery–diesel power system,” Energy,vol. 46, no. 1, pp. 168–178, Oct. 2012.

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An Adaptive Control Strategy for Low Voltage Ride Through Capability Enhancement of Grid-Connected Photovoltaic Power Plants

ABSTRACT:

This paper presents a novel application of continuous mixed -norm (CMPN) algorithm-based adaptive control strategy with the purpose of enhancing the low voltage ride through (LVRT) capability of grid-connected photovoltaic (PV) power plants. The PV arrays are connected to the point of common coupling (PCC) through a DC-DC boost converter, a DC-link capacitor, a gridside inverter, and a three-phase step up transformer. The DC-DC converter is used for a maximum power point tracking operation based on the fractional open circuit voltage method. The grid-side inverter is utilized to control the DC-link voltage and terminal voltage at the PCC through a vector control scheme. The CMPN algorithm-based adaptive proportional-integral (PI) controller is used to control the power electronic circuits due to its very fast convergence. The proposed algorithm updates the PI controller gains online without the need to fine tune or optimize. For realistic responses, the PV power plant is connected to the IEEE 39-bus New England test system. The effectiveness of the proposed control strategy is compared with that obtained using Taguchi approach- based an optimal PI controller taking into account subjecting the system to symmetrical, unsymmetrical faults, and unsuccessful reclosing of circuit breakers due to the existence of permanent fault. The validity of adaptive control strategy is extensively verified by the simulation results, which are carried out using PSCAD/EMTDC software. With the proposed adaptive-controlled PV power plants, the LVRT capability of such system can be improved

KEYWORDS:

1.      Adaptive control

2.       Low voltage ride through (LVRT)

3.       Photovoltaic (PV) power systems

4.       Power system control

5.      Power system dynamic stability

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

    

Fig. 1. Grid-connected PV power plant. (a) Connection of PV power plant. (b) Single line diagram of the IEEE 39-bus New England test system.

EXPECTED SIMULATION RESULTS:

                                  

           

 Fig. 2. Responses for 3LG temporary fault. (a) Vpcc. (b) Real power out of the PCC. (c) Reactive power out of the PCC. (d)Vdc. (e) Voltage at bus 18. (f) Inverter currents with the proposed controller.

                             

         

Fig. 3. Vpcc response for unsymmetrical faults. (a) 2LG fault. (b) LL fault. (c) 1LG fault.

                  

                         

Fig. 4. Responses for 3LG permanent fault. (a) Vpcc. (b) Real power out of the PCC. (c) Reactive power out of the PCC. (d) Vdc.

CONCLUSION:

This paper has introduced a novel application of the CMPN algorithm-based adaptive PI control strategy for enhancing the LVRT capability of grid-connected PV power plants. The proposed control strategy was applied to the DC-DC boost converter for a maximum power point tracking operation and also to the grid-side inverter for controlling the Vpcc and Vdc. The CMPN adaptive filtering algorithm was used to update the proportional and integral gains of the PI controller online without the need to fine tune or optimize. For realistic responses, the PV power plant was connected to the IEEE 39-bus New England test system. The simulation results have proven that the system responses using the CMPN algorithm-based adaptive control strategy are faster, better damped, and superior to that obtained using Taguchi approach-based an optimal PI control scheme during the following cases:

1) subject the system to a symmetrical 3LG temporary fault;

2) subject the system to different unsymmetrical faults;

3) subject the system to a symmetrical 3LG permanent fault and unsuccessful reclosure of CBs.

It can be claimed from the simulation results that the LVRT capability of grid-connected PV power plants can be further enhanced using the proposed adaptive control strategy whatever under grid temporary or permanent fault condition. By this way, the PV power plants can contribute to the grid stability and reliability, which represents a greater challenge to the network operators. Moreover, the proposed algorithm can be also applied to other renewable energy systems for the same purpose.

REFERENCES:

[1] PV Power Plants 2014 Industry Guide [Online]. Available: http://www. pvresources.com

[2] D. L. Brooks and M. Patel, “Panel: Standards & interconnection requirements for wind and solar generation NERC integrating variable generation task force,” in Proc. IEEE Power Eng. Soc. General Meeting 2011, Jul. 2011, pp. 1–3.

[3] G. J. Kish, “Addressing future grid requirements for distributed energy resources,” M.Sc. thesis, Dept. Elect. Comput. Eng., Univ. Toronto, Toronto, ON, Canada, 2011.

[4] Y. Yang, F. Blaabjerg, and Z. Zou, “Benchmarking of grid fault modes in single-phase grid-connected photovoltaic systems,” IEEE Trans. Ind. Applicat., vol. 49, no. 5, pp. 2167–2176, Sep./Oct. 2013.

[5] Y. Yang, F. Blaabjerg, and H. Wang, “Low-voltage ride-through of single-phase transformerless photovoltaic inverters,” IEEE Trans. Ind. Applicat., vol. 50, no. 3, pp. 1942–1952, May/Jun. 2014.